On Mon, 2015-07-13 at 12:02 +0200, Vincent wrote:

Hello, here are my two questions:

1- First, what kind of different storages the Caldav RFC accepts? I
was not able to retrieve this information, because lot of people seem
confused between these four words: notes, memos, tasks and todo.

CalDAV supports VEVENT (events), VTODO (tasks, also called todos),
VJOURNAL (notes or memos).

2- Second, SyncEvolution support two different backends for the things
I understand to be the same concept, and give this description in the
documentation:
      * memo: plain text notes
      * todo: task list
    So what is the difference between memo and todo?

A memo is basically just a chunk of text. VJOURNAL is a bit more than
that and also defines some additional attributes like a summary and a
date + time.

A VTODO is similar, but in addition also has fields for e.g. storing
completion progress.